Hard to believe that drinking a cup of coffee after midday can keep you awake after midnight.
But I read research showing the effect of that caffeine fix in the middle of the day lasts for more than 12 hours.
Now I never drink coffee after noon.
So far so good. But the new research says it’s more tricky than that.
Scientists have shown caffeine is more than just a stimulant – it actually slows down the body’s internal clock.
You’ll find it harder to nod off after a double espresso three hours before bedtime because the caffeine delays the production of the sleep hormone melatonin by about 40 minutes.
Dr John O’Neill, from the Medical Research Council Cambridge, has collaborated with the University of Colorado in the US to examine what’s going on.
For his part of the study, Dr O’Neill grew cells in a lab that were exposed to caffeine. He wanted to know how caffeine changed their ability to keep time.
And he found it was able to alter the chemical clocks ticking away in every cell of our body.
In Colorado, meanwhile, five people were holed up in a sleep laboratory for 50 days.
During this time scientists showed that an evening dose of caffeine slowed the body clock by 40 minutes. That means it has roughly half the impact of three hours of bright light at bedtime.
Researchers think the findings may help treat some sleep disorders and people who are up too early – often described as larks – to help them sync in with the rest of the world.
It might also be useful for jet lag. So if you’re flying across the Atlantic taking caffeine at the right time of day might speed up the time it takes you to overcome jet lag.
Prof Derk-Jan Dijk, from the University of Surrey , says: “Individuals differ in their sensitivity to caffeine and if coffee drinkers experience problems falling asleep, they may try to avoid drinking coffee in the afternoon and evening.”
He added that people often think of themselves as a “slave” to their body clocks and are programmed to wake up early or late.
“These and other data clearly indicate that we can to some extent modify these rhythms and that part of the reason why we sleep so late relates to factors such as caffeine intake and the exposure to artificial light in the evening,” he said.
So ditch that after-dinner espresso – it’ll scramble your body clock for days.
